Annealing furnaces tend to be highly inefficient in that a large quantity of heat energy generated by combustion of fuel is lost without being transferred to the work. For example, many slab reheat and annealing furnaces have placed emphasis principally on the heat transfer by radiation and the furnace geometry, the type of refractory surfaces used and the combustion techniques involved tend to make radiant heat transfer dominant. There is, accordingly, a significant convective contribution from the products of combustion which is lost. Additionally, annealing furnaces are frequently large and involve a considerable thermal inertia, slow temperature response and difficulty in handling transfer of the work. Most frequently work is held in the unit for a period of time during which it is raised to the treating temperature.
It is accordingly a general object of this invention to produce a furnace for heating, annealing or heat treating flat metal slabs or strips which is highly efficient and therefore results in economical use of fuel.
It is a further object of this invention to provide a heat treating furnace for metal stock which transfers heat to the metal stock both by convection and radiation under circumstances where both the convective contribution and the radiant contribution are substantial.
It is also an object of this invention to provide a method of heating metal stock by directing jets of combustin products onto the metal stock through a heat radiating refractory plate.
It is an additional object of the present invention to provide a method of heat treating metal stock which comprises continuously advancing the stock through an elongated combustion chamber and directing turbulent jets of combustion products onto the stock, while subjecting the stock to radiation from a perforated refractory plate through which the jets are formed.